Speaking from Chennai after he was awarded the 500,000-rupee prize at a ceremony last night, Joseph said he was "really happy" to have won the award, although the book has divided opinions. While the reception of the novel within India has generally been very good, Joseph confessed that some readers "tell me they hate it".

"Indian writers in English usually take a very sympathetic and compassionate view of the poor, and I find that fake and condescending," he explained.

Serious Men tells the story of Ayyan Mani, a middle-aged Dalit (someone of a lower caste), who works as an assistant to a brilliant Brahmin (upper-caste) astronomer at a scientific institute in Mumbai. Furious at his humble situation in life, Ayyan develops an outrageous story that his 10-year-old son is a mathematical genius – a lie which becomes increasingly elaborate and out of control.

According to the author, some readers have found the morally nuanced figure of Ayyan "offensive".

"It's a class thing," he suggested. "Most Indians readers of literary fiction written in English are of a certain class, and one of the recreations of the Indian upper class is compassion for the poor. I think the poor in India are increasingly very empowered, and the time has come when the novel can portray them in a more realistic way. Ayyan is still an underdog but that is due to his circumstances, not due to his intellect or aspirations."

One of the prize judges, the novelist Shashi Deshpande, agreed, said that Joseph had "crossed a certain barrier".

"In Indian writing in English we haven't yet approached the novel in the way this man has done," she said. "He has spoken about caste. We are ignoring reality, but he has straightforwardly plunged into the mind of a Dalit man and has done it with style and panache. To have a Dalit man speak in English and make it authentic is very difficult - but Manu Joseph has done it very easily, without making it grotesque."

Deshpande saluted Joseph's fearlessness in tackling issues of caste head on. "I must tell you we tread very warily with certain issues, like class and gender. Ayyan is a chauvinist, but the character is so engaging – two of us on the judging panel were women, and neither [was] offended by the book. We were laughing so much in the judging. Manu Joseph writes about serious matters with a marvellous, light touch, which is wonderful in any writer."

She also praised the way Joseph writes about slum life without cliche – something the author attributes to the time he spent living in a poor part of Mumbai while working as a journalist. "The good thing about being a writer is that all your miseries become material," he said.

Roland Philips, the managing director of John Murray, which published Serious Men in the UK earlier this year, hailed "the freshness of the voice and storytelling" and the book's "very sly humour". The book has yet to trouble bestseller lists in the UK, but if Joseph wins prizes in this country it will make a "huge" difference to the book, he added. "For first fiction, you need something like that."

Joseph joked that a high-profile prize in the UK might alter the way the book is perceived at home. "In India, the novel is being received very well. As long as it doesn't win the Booker ..." he said. "Most Indian books that have won the Booker have not been well received in India, because the question is raised, is the novel interpreting India for foreigners, and is it a fair interpretation or an exotic one?"